U.S. patent application number 16/503317 was filed with the patent office on 2020-02-06 for laser annealing method.
The applicant listed for this patent is SAKAI DISPLAY PRODUCTS CORPORATION. Invention is credited to Kouichi Karatani, Shinji Koiwa, Takao Matsumoto, Nobutake Nodera, Akihiro Shinozuka, Masakazu Tanaka.
Application Number | 20200043729 16/503317 |
Document ID | / |
Family ID | 69228906 |
Filed Date | 2020-02-06 |
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United States Patent
Application |
20200043729 |
Kind Code |
A1 |
Tanaka; Masakazu ; et
al. |
February 6, 2020 |
LASER ANNEALING METHOD
Abstract
A laser annealing method includes: step A of providing a
substrate having an amorphous semiconductor film formed on a
surface thereof; and step BF of selectively irradiating a portion
of the amorphous semiconductor film with laser light. Step B
includes a step of simultaneously forming, in said portion, a first
melted region that is elongated in a first direction and a second
direction that is elongated in a second melted region different
from the first direction.
Inventors: |
Tanaka; Masakazu; (Osaka,
JP) ; Koiwa; Shinji; (Osaka, JP) ; Karatani;
Kouichi; (Osaka, JP) ; Shinozuka; Akihiro;
(Osaka, JP) ; Nodera; Nobutake; (Osaka, JP)
; Matsumoto; Takao; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAKAI DISPLAY PRODUCTS CORPORATION |
Osaka |
|
JP |
|
|
Family ID: |
69228906 |
Appl. No.: |
16/503317 |
Filed: |
July 3, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/02686 20130101;
H01L 21/02691 20130101; H01L 21/0268 20130101; H01L 21/02532
20130101; H01L 21/02595 20130101 |
International
Class: |
H01L 21/02 20060101
H01L021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2018 |
JP |
2018-143165 |
Claims
1-4. (canceled)
5. A laser annealing method comprising: step A of preparing a
substrate having an amorphous semiconductor film formed on a
surface thereof; and step B of irradiating the amorphous
semiconductor film with laser light a plurality of times through a
mask having a plurality of openings while moving the substrate
relative to the mask, wherein step B includes a step of
simultaneously forming a first molten region having a shape
elongated in a first direction and a second molten region having a
shape elongated in a second direction which is different from the
first direction.
6. A laser annealing method comprising: step A of preparing a
substrate having an amorphous semiconductor film formed on a
surface thereof; and step B of forming a plurality of
polycrystalline regions by irradiating the amorphous semiconductor
film with laser light a plurality of times through a mask having a
plurality of openings while moving the substrate relative to the
mask so as to partially melt-crystallize the amorphous
semiconductor film, wherein the plurality of polycrystalline
regions include a first polycrystalline region that has a shape
elongated in a first direction and a second polycrystalline region
that has a shape elongated in a second direction which is different
from the first direction and step B includes a step of
simultaneously forming a first molten region to be the first
polycrystalline region and a second molten region to be the second
polycrystalline region.
7. The laser annealing method of claim 6, wherein the first
polycrystalline region and the second polycrystalline region are
adjacent to each other.
8. The laser annealing method of claim 6, wherein the second
direction is perpendicular to the first direction, and the
plurality of polycrystalline regions further include two third
polycrystalline regions each of which is adjacent to the first
polycrystalline region and has an elongated shape in the first
direction, and wherein step B includes, a step of simultaneously
forming two third molten regions to be the two third
polycrystalline regions.
9. The laser annealing method of claim 8, wherein step B includes,
after forming the first polycrystalline region, a step of
irradiating a region of the amorphous semiconductor film including
the first polycrystalline region with the laser light so as to
simultaneously form the two third molten regions to be the two
third polycrystalline regions.
10. The laser annealing method of claim 6, wherein the second
direction is perpendicular to the first direction, and the
plurality of polycrystalline regions further include two fourth
polycrystalline regions each of which is adjacent to the second
polycrystalline region and has an elongated shape in the second
direction, and wherein step B includes a step of simultaneously
forming two fourth molten regions to be the two fourth
polycrystalline regions.
11. A laser annealing method of claim 10, wherein step B includes,
after forming the second polycrystalline region, a step of
irradiating a region of the amorphous semiconductor film with the
laser light which includes the second polycrystalline region so as
to simultaneously form the two fourth molten regions to be the
fourth polycrystalline regions.
12. A laser annealing method comprising: step A of preparing a
substrate having an amorphous semiconductor film formed on a
surface thereof; and step B of forming a plurality of
polycrystalline regions by irradiating the amorphous semiconductor
film with laser light a plurality of times through a mask having a
plurality of openings while moving the substrate relative to the
mask so as to partially melt-crystallize the amorphous
semiconductor film, wherein the plurality of polycrystalline
regions include a first polycrystalline region that has a shape
elongated in a first direction and a second polycrystalline region
that is adjacent to the first polycrystalline region, and step B
includes a step of irradiating a molten region to be the second
polycrystalline region with the laser light a plurality of
times.
13. The laser annealing method of claim 12, wherein the substrate
is moved relative to the mask in the first direction.
14. The laser annealing method of claim 12, wherein the substrate
is moved relative to the mask in a direction perpendicular to the
first direction.
Description
BACKGROUND
1. Technical Field
[0001] The present invention relates to a laser annealing
apparatus, a display panel, a laser annealing method and a
mask.
2. Description of the Related Art
[0002] While examples of TFTs (Thin Film Transistors) of liquid
crystal displays include amorphous silicon (non-crystalline, a-Si)
TFTs and low temperature polysilicon (polycrystalline, p-Si) TFTs,
for example, polycrystalline silicon has been often used instead of
amorphous silicon in cases where there is a demand for high-speed
operations such as with driver circuits, etc.
[0003] For crystallization of semiconductor film regions on the
substrate, a process is known in the art for growing grain
boundaries in the lateral direction parallel to the substrate
surface by using a sequential lateral solidification (SLS) method.
In the conventional SLS method, intended regions of a silicon film
are irradiated with laser light through thin slit openings of a
mask so as to completely melt the silicon of the regions, and the
molten silicon is then re-solidified. When the molten silicon is
re-solidified, grain boundaries grow in the direction of the thin
width of the thin-slit irradiated regions corresponding to the
openings. Then, by repeatedly shifting regions to be irradiated
with laser light by shifting the substrate, it is possible to grow
grain boundaries in the substrate shift direction (the scanning
direction) (Patent Document No. 1: see Japanese National Phase PCT
Laid-Open Publication No. 2000-505241).
SUMMARY
[0004] However, with the conventional SLS method, the growth
direction of grain boundaries is limited to the substrate scanning
direction, and it is not possible to grow grain boundaries in an
arbitrary direction.
[0005] The present invention has been made in view of the above,
and an object thereof is to provide a laser annealing apparatus
capable of producing grain boundaries in an intended direction, a
display panel manufactured by the laser annealing apparatus, a
laser annealing method, and a mask that is a part of the laser
annealing apparatus.
[0006] A laser annealing apparatus according to an embodiment of
the present invention is a laser annealing apparatus including a
mask having an opening row, wherein the opening row includes
openings each including an opening region and arranged in a
scanning direction, for irradiating a substrate with laser light
through the openings, wherein: a first opening including a first
opening region and a second opening including a second opening
region are arranged next to each other in a direction parallel to
the scanning direction; and the mask has a first opening row in
which the second opening region includes an opening region that is
obtained by displacing a region corresponding to the first opening
region at the second opening in a predetermined direction different
from the scanning direction.
[0007] A display panel according to an embodiment of the present
invention includes thin film transistors having active layers
annealed by the laser annealing method according to an embodiment
of the present invention.
[0008] A mask according to an embodiment of the present invention
is a mask having an opening row, wherein the opening row includes
openings each including an opening region and arranged in a
scanning direction, wherein: a first opening including a first
opening region and a second opening including a second opening
region are arranged next to each other in a direction parallel to
the scanning direction; and the mask has an opening row in which
the second opening region includes an opening region that is
obtained by displacing a region corresponding to the first opening
region at the second opening in a predetermined direction different
from the scanning direction.
[0009] A laser annealing method according to an embodiment of the
present invention includes: step A of providing a substrate having
an amorphous semiconductor film formed on a surface thereof; and
step B of selectively irradiating a portion of the amorphous
semiconductor film with laser light, wherein step B includes a step
of simultaneously forming, in said portion, a first melted region
that is elongated in a first direction and a second direction that
is elongated in a second melted region different from the first
direction.
[0010] According to the present invention, grain boundaries can be
made to grow in intended directions, without being limited to the
substrate scanning direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic view showing an example configuration
of a laser annealing apparatus of the present embodiment.
[0012] FIG. 2 is a schematic plan view showing an example
configuration of a mask of the present embodiment.
[0013] FIG. 3 is a schematic view showing the positional
relationship between openings and microlenses of the present
embodiment.
[0014] FIG. 4A is a schematic view showing an example of a
substrate scanning operation of the laser annealing apparatus of
the present embodiment.
[0015] FIG. 4B is a schematic view showing an example of a
substrate scanning operation of the laser annealing apparatus of
the present embodiment.
[0016] FIG. 4C is a schematic view showing an example of a
substrate scanning operation of the laser annealing apparatus of
the present embodiment.
[0017] FIG. 5 is a schematic view showing a first example of
openings of a mask portion of the present embodiment.
[0018] FIG. 6 is a schematic view showing an example of how an
amorphous silicon film grows using a laser annealing apparatus of
the present embodiment.
[0019] FIG. 7 is a schematic view showing a second example of
openings of a mask portion of the present embodiment.
[0020] FIG. 8 is a schematic view showing an example of a display
panel including thin film transistors that are annealed by a laser
annealing apparatus of the present embodiment.
[0021] FIG. 9 is a schematic view showing another example of a
display panel including thin film transistors that are annealed by
a laser annealing apparatus of the present embodiment.
[0022] FIG. 10 is a schematic view showing a third example of
openings of a mask portion of the present embodiment.
[0023] FIG. 11 is a schematic view showing an example of how grain
boundaries grow in regions that are annealed by a mask portion
shown in FIG. 10.
[0024] FIG. 12 is a schematic view showing a fourth example of
openings of a mask portion of the present embodiment.
[0025] FIG. 13 is a schematic view showing an example of how grain
boundaries grow in regions that are annealed by a mask portion
shown in FIG. 12.
[0026] FIG. 14 is a flow chart showing an example of a laser
annealing method using the laser annealing apparatus of the present
embodiment.
DETAILED DESCRIPTION
[0027] The present invention will now be described with reference
to drawings that show embodiments thereof. FIG. 1 is a schematic
view showing an example configuration of a laser annealing
apparatus of the present embodiment. A laser annealing apparatus
100 of the present embodiment includes a laser light source 70 that
emits laser light, an optical system 60 that includes a group of
lenses for shaping the laser light emitted from the laser light
source 70 into a parallel beam, a mask (light-blocking plate) 30
that includes a mask portion 40 where openings and microlenses to
be described below are arranged in an array, etc. The parallel beam
shaped through the optical system 60 selectively irradiates
intended locations of a substrate 10 through the openings and the
microlenses of the mask portion 40. The substrate 10 is transferred
at a constant speed by a driving mechanism (not shown). The laser
light source 70 shoots laser light at time intervals such that
laser light is shot each time an irradiation position of the
substrate 10 arrives at a position corresponding to an opening.
Note that the laser annealing apparatus 100 may be configured so
that the mask 30, or the like, is moved while the substrate 10 is
fixed, instead of moving the substrate 10. An example where the
substrate 10 is moved will be described below.
[0028] FIG. 2 is a schematic plan view showing an example
configuration of the mask 30 of the present embodiment. The mask 30
includes the rectangular mask portion 40. The dimension of the mask
portion 40 in the scanning direction (vertical direction) is
denoted as W, and the dimension thereof in the direction (lateral
direction) perpendicular to the scanning direction as L. The mask
portion 40 includes an array of microlenses 21 arranged at regular
intervals in the scanning direction and in the direction
perpendicular to the scanning direction. Openings to be described
below are formed at predetermined positions that are the positions
of the centers of the microlenses 21 as seen from above.
[0029] The vertical dimension W of the mask portion 40 may be about
5 mm and the lateral dimension L may be about 50 mm, for example,
but these dimensions are not limited thereto. Twenty microlenses 21
are arranged at regular intervals in the scanning direction
vertical direction). Since each microlens 21 corresponds to one
opening, the mask 30 includes 20 openings arranged at regular
intervals n the scanning direction (vertical direction). In FIG. 2,
each row of 20 openings provided along the scanning direction is
referred to as an "opening row". The mask 30 includes a plurality
of opening rows arranged in the direction perpendicular to the
scanning direction.
[0030] FIG. 3 is a schematic view showing the positional
relationship between openings 50 and the microlenses 21 of the
present embodiment. FIG. 3 shows the positional relationship
between the openings 50 and the microlenses 21 as seen from above,
and also shows the position of an opening 50 with respect to the
position of the corresponding microlens 21 as seen from above. Note
that the size of the opening 50 and the size of the irradiation
pattern are drawn to be generally equal to each other in the
present embodiment for the sake of illustration. In practice,
however, laser light is converged through the microlens 21, and the
size of the opening 50 is larger than the size of the irradiation
pattern. As shown in FIG. 3, the mask portion 40 includes a
plurality of openings 50 and a plurality of microlenses (lenses)
21. Note that the microlenses 21 are formed on a transparent
substrate 20 corresponding to the openings 50, and the transparent
substrate 20 and the mask 30 are integral with each other. The
openings 50 are arranged so that the center of each microlens 21
having a circular shape as seen from above coincides with the
center of the corresponding opening 50 having a rectangular shape
as seen from above. The mask 30 and the light-receiving surface of
the microlenses 21 are appropriately spaced apart from each other.
The maximum size of the microlens 21 (the diameter of the circular
shape as seen from above) may be set to about 150 .mu.m to about
400 .mu.m, for example, but is not limited thereto. A collection of
microlenses 21 will be referred to also as a "microlens array".
Note that an opening 50 is herein also referred to simply as an
"opening", which includes one or more opening regions.
[0031] When the parallel beam shaped through the optical system 60
described above hits an opening 50 of the mask portion 40, the
laser light having passed through the corresponding opening 50 is
converged through the microlens 21, and the converged laser light
selectively irradiates an intended location on the substrate 10
that corresponds to the opening 50 (i.e., the microlens 21). The
intended location is typically a region to be a semiconductor layer
(which may be referred to also as an "active layer") of one TFT. As
shown in FIG. 6, etc., a semiconductor layer (active layer) of one
TFT includes a channel region, a source region and a drain
region.
[0032] FIG. 4A, FIG. 4B and FIG. 4C are schematic views showing an
example scan of the substrate 10 by the laser annealing apparatus
100 of the present embodiment. FIG. 4A shows a state where the mask
30 is set at a predetermined position, showing a state before the
movement of the substrate 10 in the scanning direction is started.
From the state shown in FIG. 4A, the substrate 10 is moved in the
scanning direction at a constant speed. The laser light source 70
shoots laser light at time intervals such that laser light is shot
each time an irradiation position of the substrate 10 arrives at a
position corresponding to an opening 50. For example, with the
openings 50 illustrated in FIG. 2, the same location of the
substrate 10 is irradiated with laser light 20 times. FIG. 4B shows
a state where the substrate 10 has been moved at a constant speed
to the final position in the scanning direction (i.e., over the
distance Z). By moving the substrate 10 to the state shown in FIG.
4B, the intended locations within an irradiation region S on the
substrate 10 can be selectively irradiated with laser light as
shown in FIG. 4C. In the state shown in FIG. 4C, by moving the mask
30 over the distance L in the direction perpendicular to the
scanning direction, and moving the substrate 10 in the scanning
direction as shown in FIG. 4A and FIG. 4b, it is possible to
increase the irradiation region S. Note that while the size of the
substrate 10 and the size of the mask 30 are shown to be similar to
each other in FIG. 4, the size of the substrate 10 is in practice
far larger than that shown in FIG. 4.
[0033] Next, the mask portion 40 of the mask 30 of the present
embodiment will be described in detail. FIG. 5 is a schematic view
showing a first example of openings of the mask portion 40 of the
present embodiment. In the example below, for the sake of
illustration, the mask portion 40 includes four different openings
a, b, c and d provided along the direction parallel to the scanning
direction. While four different openings a, b, c and d are shown to
be adjacent to each other in the scanning direction in FIG. 5, this
does not represent the positions of the openings in the scanning
direction.
[0034] Each of the openings a, b, c and d is provided in the
vicinity of a central position 54 of the corresponding one of the
microlenses 21. Where the diameter of the microlens 21 is 250
.mu.m, for example, each of the openings a, b, c and d is formed
within a radius of 10 .mu.m to 20 .mu.m from the central position
54 of the corresponding microlens 21. The range over which the
openings a, b, c and d are formed can be set appropriately so that
the microlenses 21 can project, in reduced projection, with a
sufficient precision the images of the openings a, b, c and d onto
the surface of the semiconductor film. The number of times the
semiconductor film is irradiated with laser light to melt the
semiconductor film depends on the laser light irradiation energy
density.
[0035] For example, the microlens array shown in FIG. 2 includes 20
(20 rows) of microlens 21 arranged in the scanning direction. The
four different openings a, b, c and d are arranged corresponding to
the 20 microlenses 21. For example, the opening a is arranged
corresponding to microlenses 21 of the first row (the bottom row in
FIG. 2) to the fifth row in the scanning direction, the opening b
is arranged corresponding to microlenses 21 of the sixth row to the
tenth row, the opening c is arranged corresponding to microlenses
21 of the eleventh row to the fifteenth row, and the opening d is
arranged corresponding to microlenses 21 of the sixteenth row to
the twentieth row.
[0036] Using the mask 30 including the four different openings a,
b, c and d arranged as described above, regions of the
semiconductor film to be the active layers of the TFTs are
irradiated with laser light 20 times while moving the microlens
array including 20 rows of microlenses 21 row by row relative to
the substrate 10. Then, the region corresponding to the opening a
is irradiated with laser light for the first to fifth shots, the
region corresponding to the opening b is irradiated with laser
light for the sixth to tenth shots, the region corresponding to the
opening c is irradiated with laser light for the eleventh to
fifteenth shots, and the region corresponding to the opening d is
irradiated with laser light for the sixteenth to twelfth shots.
That is, this example is a case where the amorphous semiconductor
film is melted by being irradiated with laser light five times.
[0037] Needless to say, the arrangement of the four different
openings a, b, c and d is not limited to that illustrated herein.
For example, the order of the four different openings a, b, c and d
may be changed (e.g., the opening b for the first to fifth rows,
the opening a for the sixth to tenth rows, the opening d for the
eleventh to fifteenth rows, and the opening c for the sixteenth to
twenties rows). Note that the region that is crystallized by laser
light irradiation (the polycrystalline region) is not melted unless
it is heated to its melting point or higher. The temperature for
melt-crystallizing the amorphous semiconductor film is lower than
the melting point of the polycrystalline, and the laser light
irradiation energy density, the irradiation time and the number of
times of irradiation for melt-crystallizing an amorphous
semiconductor film are set so that the semiconductor film is not
heated to or above the melting point of the polycrystalline.
Therefore, when the arrangement of the openings a, b, c and d is
changed, the regions to be melt-crystallized will vary in
accordance with the arrangement of the openings a, b, c and d.
[0038] The number of rows of the microlens array does not need to
be 20 rows, but it may be four rows or more than 20 rows. It may be
changed as necessary taking into consideration the laser light
irradiation energy density, the oscillation time, the
light-converging ability of microlenses and the reduction rate that
is determined based on the distance between the microlenses and the
semiconductor film, etc.
[0039] Each of the openings a, b, c and d includes a plurality of
opening regions. Each of the openings a, b, c and d illustrated
herein includes opening regions corresponding to the channel region
(middle), the drain region (upper or lower) and the source region
(lower or upper). Openings 52a, 52b, 52c and 52d for forming the
channel region each have a rectangular shape that is elongated in
the scanning direction (having a smaller width in the direction
perpendicular to the scanning direction), whereas openings 51a,
51b, 51c and 51d for forming the drain region and openings 53a,
53b, 53c and 53d for forming the source region each have a
rectangular shape that is elongated in the direction perpendicular
to the scanning direction (having a smaller width in the scanning
direction).
[0040] Thus, according to the embodiment of the present invention,
the mask includes two or more opening regions that are elongated in
two different directions, and regions of the semiconductor film
corresponding to the opening regions are selectively irradiated
with laser light and melted. That is, the regions of the
semiconductor film corresponding to the opening regions (i.e., the
regions onto which the opening regions are projected in reduced
projection) are melted. The regions of the semiconductor film
corresponding to the opening regions that are irradiated with laser
light and melted may be referred to as the "melted regions". The
shape of a melted region is similar to the shape of the
corresponding opening region. By the irradiation with laser light
through two or more opening regions that are elongated in different
directions, there are formed two or more elongate melted regions
arranged in different directions, and it is therefore possible to
form a semiconductor layer including a plurality of crystalline
regions whose grain boundaries extend in different directions.
[0041] The plurality of opening regions of each of the openings a,
b, c and d include opening regions corresponding to the channel
region (middle), the drain region (upper or lower) and the source
region (lower or upper). That is, a plurality opening regions of
each of the openings a, b, c and d can be expressed as three
opening rows A, B and C as shown in FIG. 5. Needless to say, the
number of opening rows of the mask according to the embodiment of
the present invention and the number of openings in each opening
row are not limited to those of the example of FIG. 5.
[0042] As shown in FIG. 5, each of the opening rows A, B and C
includes the openings a, b, c and d arranged in the scanning
direction. The opening row B can be referred to as the first
opening row, and the opening row A and the opening row C can be
referred to as the second opening row. Where the opening a is
regarded as the first opening, the opening b can be regarded as the
second opening. The relationship between the opening b and the
opening c and the relationship between the opening c and the
opening d are also similar to the relationship between the opening
a and the opening b.
[0043] As shown in FIG. 5, in the opening row A (referred to also
as the "second opening row"), the opening a includes the opening
region 51a, the opening b includes the opening region 51b, the
opening c includes the opening region 51c, and the opening d
includes the opening region 51d. In the opening row B, the opening
a includes the opening region 52a, the opening b includes the
opening region 52b, the opening c includes the opening region 52c,
and the opening d includes the opening region 52d. Similarly, in
the opening row C, the opening a includes the opening region 53a,
the opening b includes the opening region 53b, the opening c
includes the opening region 53c, and the opening d includes the
opening region 53d. In each row, the opening a includes only one
opening region, and the openings b to d each include only two
opening regions.
[0044] Each of the opening regions of the opening row A and the
opening row C has a rectangular shape. More specifically, the
opening regions 51a to 51d and 53a to 53d each have a shape
elongated in the direction perpendicular to the scanning direction.
Each of the opening regions of the opening row B also has a
rectangular shape. More specifically, the opening regions 52a to
52d each have a shape elongated in the scanning direction. Note
that the shapes of the opening regions of FIG. 5 are shown for the
sake of illustration, and the actual opening regions may have
shapes different from those shown in FIG. 5. The width (the
dimension in the scanning direction) of the opening regions 51a to
51d and 53a to 53d may be some .mu.m, for example. The width (the
dimension in the direction perpendicular to the scanning direction)
of the opening regions 52a to 52d may be some .mu.n, for
example.
[0045] An elongated rectangular shape as used herein refers to a
shape whose aspect ratio (long side/short side) is three or more,
and the length of the short side is 4 .mu.m or less, for example.
If the length of the short side exceeds 4 .mu.m, the lateral growth
may not reach the center of the melted region during
crystallization, resulting in microcrystals occurring in the middle
of the melted region. Note that the shape of each opening region is
not limited to a rectangular shape, but may be an elliptical shape,
for example, in which case the aspect ratio can be defined as major
axis/minor axis. An opening region may have a shape other than a
rectangular shape or an elliptical shape, in which case the shape
is preferably line-symmetrical with respect to the major axis and
the minor axis.
[0046] In the opening row B, where the opening a is regarded as the
first opening and the opening b as the second opening, the opening
region 52a (the first opening region) and the opening region 52b
(the second opening region) are arranged next to each other in the
direction parallel to the scanning direction. When opening regions
are shifted so that the central position 54 of the opening a
coincides with the central position 54 of the opening b, the
opening region 52b includes an opening region that is obtained by
displacing a region corresponding to the opening region 52a at the
opening b (the second opening) in the direction perpendicular to
the scanning direction.
[0047] Similarly, in the opening row B, where the opening b is
regarded as the first opening and the opening c as the second
opening, the opening region 52b (the first opening region) and the
opening region 52c (the second opening region) are arranged next to
each other in the direction parallel to the scanning direction.
When opening regions are shifted so that the central position 54 of
the opening b coincides with the central position 54 of the opening
c, the opening region 52c includes an opening region that is
obtained by displacing a region corresponding to the opening region
52b at the opening c (the second opening) in the direction
perpendicular to the scanning direction. The relationship between
the opening c and the opening d is similar to this.
[0048] In the opening row A, when the opening a is regarded as the
first opening and the opening b as the second opening, the opening
region 51a (the first opening region) and the opening region 51b
(the second opening region) are arranged next to each other in the
direction parallel to the scanning direction. When opening regions
are shifted so that the central position 54 of the opening a
coincides with the central position 54 of the opening b, the
opening region 51b includes an opening region that is obtained by
displacing a region corresponding to the opening region 51a at the
opening b (the second opening) in the direction parallel to the
scanning direction.
[0049] Similarly, in the opening row A, where the opening b is
regarded as the first opening and the opening c as the second
opening, the opening region 51b (the first opening region) and the
opening region 51c (the second opening region) are arranged next to
each other in the direction parallel to the scanning direction.
When opening regions are shifted so that the central position 54 of
the opening b coincides with the central position 54 of the opening
c, the opening region 51c includes an opening region that is
obtained by displacing a region corresponding to the opening region
51b at the opening c (the second opening) in the direction parallel
to the scanning direction. The relationship between the opening c
and the opening d is similar to this. The opening row C is similar
to the opening row A.
[0050] Although four openings a, b, c and d are arranged adjacent
to each other in the scanning direction in the description above,
five of each of the openings a, b, c and d may be arranged in the
scanning direction as described above with reference to FIG. 2.
Even in such a case, there are a location where the opening a and
the opening b are adjacent to each other, a location where the
opening b and the opening c are adjacent to each other, and a
location where the opening c and the opening d are adjacent to each
other, as described above.
[0051] Next, grain boundaries will be described. When an amorphous
silicon (non-crystalline, a-Si) film is irradiated with laser
light, the amorphous silicon film is hot-melted. The crystal growth
advances with the hot-melted amorphous silicon solidifying inwardly
from the laser light irradiation region boundary. The crystallized
region of the semiconductor film has a structure (polycrystal line
structure) that is a collection of many regions (referred to also
as the "crystal grains") where atoms are arranged in different
directions, and boundaries between crystal grains are referred to
as grain boundaries. Where the laser light irradiation region is an
elongate rectangular shape, crystals that grow from the opposing
boundaries along the width direction inwardly come close to each
other, resulting in the direction of grain boundaries being
generally the width direction. Note that since the directions of
individual grain boundaries vary, the direction of a grain boundary
as used herein means the average direction among the grain
boundaries included in the crystallized region, referring to the
general direction of the crystal grains as a whole.
[0052] FIG. 6 is a schematic view showing an example of how an
amorphous silicon film grows using the laser annealing apparatus
100 of the present embodiment. The crystal growth shown in FIG. 6
is an example where the openings shown in FIG. 5 are used.
[0053] FIG. 6 shows the channel region, the region (the source
region) directly under the source electrode and the region (the
drain region) directly under the drain electrode, which are on the
opposite sides of the channel region. The reference sign 11 denotes
an amorphous silicon film, and the reference sign 12 denotes a
polysilicon film. The reference sign 13 denotes grain boundaries.
FIG. 6 schematically shows how crystals grow in the amorphous
silicon film, which is the laser light irradiation region, showing,
left to right, how crystals grow over the number of iterations of
laser light irradiation (from the first iteration to the fourth
iteration). Note that the first iteration is when laser light is
shot through the opening a, the second iteration is when laser
light is shot through the opening b, the third iteration is when
laser light is shot through the opening c, and the fourth iteration
is when laser light is shot through the opening d. Where laser
light is shot five times, for example, through each of the openings
a, b, c and d, the figure schematically shows grain boundaries
after the fifth not.
[0054] The first iteration in FIG. 6 shows the crystal growth in
the irradiation region when laser light is shot through the opening
a shown in FIG. 5. The opening region 52a has a rectangular shape
elongated in the direction parallel to the scanning direction
(referred to also as the "lateral direction"), and the width
dimension thereof along the direction perpendicular to the scanning
direction (which is referred to also as the vertical direction) is
small. Therefore, the hot-melted amorphous silicon film 11
solidifies inwardly from the opposing boundaries in the lateral
direction of the irradiation region corresponding to the opening
region 52a, forming the polysilicon film 12. In this case, the
direction of grain boundaries 13 is the vertical direction.
[0055] The opening region 51a has a rectangular shape elongated in
the vertical direction and the width dimension thereof along the
lateral direction is small. Therefore, the hot-melted amorphous
silicon film 11 solidifies inwardly from the opposing boundaries in
the vertical direction of the irradiation region corresponding to
the opening region 51a, forming the polysilicon film 12. In this
case, the direction of grain boundaries 13 is the lateral
direction. With the opening region 53a, similar to the opening
region 51a, the film solidifies inwardly from the opposing
boundaries in the vertical direction of the irradiation region
corresponding to the opening region 53a, forming the polysilicon
film 12. In this case, the direction of grain boundaries 13 is the
lateral direction.
[0056] The second iteration shows the crystal growth in the
irradiation region when laser light is shot through the opening b
shown in FIG. 5. The opening region 52b includes two opening
regions spaced apart from each other in the vertical direction with
a region corresponding to the opening region 52a interposed
therebetween, and the opening region 52b forms a rectangular shape
elongated in the lateral direction and the width dimension thereof
along the vertical direction is small. Therefore, the hot-melted
amorphous silicon film 11 solidifies inwardly from the opposing
boundaries in the lateral direction of the irradiation region
corresponding to the opening region 52b, forming the polysilicon
film 12. In this case, the direction of grain boundaries 13 is the
vertical direction.
[0057] The opening region 51b includes two opening regions spaced
apart from each other in the lateral direction with a region
corresponding to the opening region 51a interposed therebetween,
and the opening region 51b forms a rectangular shape elongated in
the vertical direction and the width dimension thereof along the
lateral direction is small. Therefore, the hot-melted amorphous
silicon film 11 solidifies inwardly from the opposing boundaries in
the vertical direction of the irradiation region corresponding to
the opening region 51b, forming the polysilicon film 12. In this
case, the direction of grain boundaries 13 is the lateral
direction. With the opening region 53b, similar to the opening
region 51b, the film solidifies inwardly from the opposing
boundaries in the vertical direction of the irradiation region
corresponding to the opening region 53b, forming the polysilicon
film 12. In this case, the direction of grain boundaries 13 is the
lateral direction.
[0058] As the laser light irradiation is repeated for the third
iteration and the fourth iteration as shown in FIG. 6, the
direction of grain boundaries in the channel region is parallel to
the longitudinal direction of the channel region (i.e., the
direction perpendicular to the scanning direction), and the
direction of grain boundaries in the region directly under the
drain electrode and the region directly under the source electrode
is the direction perpendicular to the longitudinal direction of the
channel region (i.e., the scanning direction), as shown in "Fourth
iteration" in FIG. 6.
[0059] In grain boundaries, electrons tend to be scattered,
resulting in a low electron mobility. In the channel region, since
the direction of grain boundaries is the longitudinal direction of
the channel region, the degree by which electrons are scattered by
grain boundaries is small, and it is possible to realize a large ON
current of the thin film transistor. In regions directly under the
source electrode and the drain electrode, the direction of grain
boundaries is the direction perpendicular to the longitudinal
direction of the channel region, for example, and it is therefore
possible to increase the frequency with which electrons pass
through grain boundaries and reduce the OFF current of the thin
film transistor.
[0060] As described above, in the opening row B (the first opening
row), the irradiation region of the semiconductor film is
irradiated with laser light through the opening region 52a, and
grain boundaries in the region irradiated with laser light grow in
a predetermined direction (e.g., the direction perpendicular to the
scanning direction). At the point in time for the next laser light
irradiation, the irradiation region is irradiated with laser light
through the opening region 52b. In this case, since the opening
region 52b includes an opening region that is obtained by
displacing the region corresponding to the opening region 52a in a
predetermined direction different from the scanning direction,
grain boundaries further grow in the predetermined direction. This
similarly applies to the opening regions 52c and 52d. Thus, grain
boundaries can be made to grow in intended directions (e.g., the
direction perpendicular to the scanning direction), without being
limited to the substrate scanning direction.
[0061] As described above, in the opening row A (the second opening
row), the irradiation region of the semiconductor film is
irradiated with laser light through the opening region 51a, and
grain boundaries in the region irradiated with laser light grow in
the direction parallel to the scanning direction. At the point in
time for the next laser light irradiation, the irradiation region
is irradiated with laser light through the opening region 51b. In
this case, since the opening region 51b includes an opening region
that is obtained by displacing the region corresponding to the
opening region 51a in the direction parallel to the scanning
direction, grain boundaries further grow in the direction parallel
to the scanning direction. This similarly applies to the opening
regions 51c and 51d. The opening row C (the second opening row) is
similar to the opening row A. Thus, it is possible to produce a
structure having different grain boundaries on the same substrate.
For example, grain boundaries can be made to grow in different
directions (in the scanning direction and in the direction
perpendicular to the scanning direction in the example of FIG. 5
and FIG. 6).
[0062] In the example described above, in the opening row B, the
opening region 52b does not include a portion of the region
corresponding to the opening region 52a at the opening b. That is,
the opening region 52b is divided into two opening regions with a
portion of the region corresponding to the opening region 52a
interposed therebetween. Thus, when laser light is shot through the
opening region 52b of the opening b, a part or whole of the
crystalline semiconductor film corresponding to the region between
the two opening regions 52b (the polycrystalline semiconductor
region) may be blocked from laser light irradiation. This similarly
applies to the opening regions 52c and 52d. This similarly applies
to the opening row A and the opening row C. By performing the next
laser light irradiation so as to partially overlap with the region
crystallized by the previous laser light irradiation, crystals that
have been produced through the previous laser light irradiation can
grow continuously. Note that the region crystallized through the
previous laser light irradiation (the polycrystalline semiconductor
region) may be irradiated with laser light under conditions (the
laser light irradiation energy density, the irradiation time and
the number of times of irradiation) such that polycrystalline does
not melt even when irradiated again with laser light. This is
because grain boundaries can similarly be formed continuously.
[0063] The predetermined direction may be the direction
perpendicular to the scanning direction. Then, it is possible to
form, on the substrate surface, grain boundaries extending in the
vertical direction and grain boundaries extending in the lateral
direction.
[0064] As shown in FIG. 5, each opening region forms a rectangular
shape. In the opening row B, the opening regions 52a to 52d may be
shaped to be elongated in the direction parallel to the scanning
direction, whereas in the opening row A and the opening row C, the
opening regions 51a to 51d and 53a to 53d may be shaped to be
elongated in a predetermined direction different from the scanning
direction (the direction perpendicular to the scanning direction).
Thus, the direction of grain boundaries can be an intended
direction.
[0065] FIG. 7 is a schematic view showing a second example of the
openings 50 of the mask portion 40 of the present embodiment. In
the first example shown in FIG. 5, in the opening row B, the
opening region 52b does not include a portion of the region
corresponding to the opening region 52a at the opening b as shown
in FIG. 5, for example. That is, the opening region 52b is divided
into two opening regions with a portion of the region corresponding
to the opening region 52a interposed therebetween.
[0066] On the other hand, in the second example, in the opening row
B, an opening region 152b includes a region corresponding to an
opening region 152a at the opening b as shown in FIG. 7. That is,
the opening region 152b is a single opening region that includes a
region corresponding to the opening region 152a. Thus, when laser
light is shot through the opening region 152b of the opening b, the
region irradiated with laser light through the opening region 152a
of the opening a is irradiated again with laser light. In this
process, if the region crystallized through the previous laser
light irradiation (the polycrystalline semiconductor region) is
irradiated with laser light under conditions (the laser light
irradiation energy density, the irradiation time and the number of
times of irradiation) such that polycrystalline does not melt even
when irradiated again with laser light, it is possible to
substantially form the polycrystalline semiconductor region shown
in FIG. 6. Typical laser light irradiation conditions for
crystallizing amorphous silicon satisfy those conditions described
above. This similarly applies to opening regions 152c and 152d.
This similarly applies to the opening row A and the opening row
C.
[0067] Thus, even if the region to be irradiated with laser light
in the second or subsequent iteration includes a region that has
been previously irradiated with laser light and crystallized, the
previously crystallized region is not melted. Therefore, if an
amorphous region, of the region to be irradiated with laser light
in the second or subsequent iteration, has an elongate shape, it is
possible to form a polycrystalline semiconductor region having
grain boundaries extending in a predetermined direction. Therefore,
although the opening regions 152b, 152c and 152d of FIG. 7 do not
have a shape elongated in the lateral direction as does the opening
region 152a, it is possible to melt-crystallize the same regions as
with the pairs of opening regions 52b, 52c and 52d shown in FIG. 5.
Similarly, although opening regions 151b, 151c and 151d of FIG. 7
do not have a shape elongated in the vertical direction as does an
opening region 151a, it is possible to melt-crystallize the same
regions as with the pairs of opening regions 51b, 51c and 51d shown
in FIG. 5. Although opening regions 153b, 153c and 153d of FIG. 7
do not have a shape elongated in the vertical direction as does an
opening region 153a, it is possible to melt-crystallize the same
regions as with the pairs of opening regions 53b, 53c and 53d shown
in FIG. 5.
[0068] FIG. 8 is a schematic view showing an example of a display
panel 200 including thin film transistors having active layers
annealed by the laser annealing apparatus 100 of the present
embodiment. The crystallization through laser light irradiation
described above is referred to as an annealing process.
[0069] The display panel 200 includes a rectangular pixel region
201, and a peripheral circuit section 202 provided around the pixel
region 201, etc. One of the two designations "SD" refers to the
source electrode (&) and the other refers to the drain
electrode (D). In a GOA (Gate Driver On Array) circuit section 212
in the peripheral circuit section 202, the direction of grain
boundaries in the channel region between the source electrode and
the drain electrode may be the lateral direction, and in a pixel
portion 211 of the pixel region 201, the direction of grain
boundaries in the channel region between the source electrode and
the drain electrode may be the vertical direction. Thus, the
direction of grain boundaries can be varied between the pixel
portion and the peripheral circuit. That is, two different thin
film transistors, of which the longitudinal directions of the
channel regions are perpendicular to each other, can be formed on
the same substrate. Therefore, the positions of the drain electrode
and the source electrode with respect to the channel region can be
changed freely in the vertical direction and in the lateral
direction, and it is possible to increase the degree of freedom in
designing circuits on the substrate. It is possible to realize a
display panel having thin film transistors, wherein grain
boundaries are made to grow in intended directions, without being
limited to the substrate scanning direction.
[0070] FIG. 9 is a schematic view showing another example of
display panels 200 including thin film transistors having active
layers annealed by the laser annealing apparatus 100 of the present
embodiment. The example of FIG. 9 shows how two display panels 200
are produced from a single glass substrate. Each display panel 200
includes the rectangular pixel region 201, and the peripheral
circuit section 202 provided around the pixel region 201, etc. The
pixel region 201 of the upper display panel 200 includes a group of
thin film transistors 220, wherein the direction of grain
boundaries 13 in the channel region is the vertical direction. The
pixel region 201 of the lower display panel 200 includes a group of
thin film transistors 230, wherein the direction of grain
boundaries 13 in the channel region is the lateral direction. Thus,
the direction of grain boundaries can be varied within a substrate.
Since the direction of grain boundaries can be set to any
direction, an experiment on the direction of grain boundaries can
be performed at once within a substrate.
[0071] FIG. 10 is a schematic view showing a third example of the
openings 50 of the mask portion 40 of the present embodiment.
Opening regions 251a to 251d of the opening row A are similar to
the opening regions 151a to 151d of the second example shown in
FIG. 7. Opening regions 253a to 253d of the opening row C are
similar to the opening regions 153a to 153d of the second example
shown in FIG. 7. A difference from the second example is that
opening regions 252a to 252d of the opening row B have a
rectangular shape of the same size, and have generally the same
vertical and lateral dimensions as those of the channel region.
[0072] FIG. 11 is a schematic view showing an example of how grain
boundaries grow in regions that are crystallized using the mask
portion 40 shown in FIG. 10. When repeatedly irradiated with laser
light through the opening regions 252a to 252d of the opening row
B, there are formed polycrystalline regions in the channel region
where grain boundaries 14 extend in the thickness direction (the
direction from the near side toward the far side on the drawing
sheet, i.e., the direction toward the gate electrode), as shown in
FIG. 11. Since the size of the opening regions 252a to 252d is
large, the lateral growth does not reach the central ort ion of the
melted region during crystallization, resulting in microcrystals
formed in much of the melted region. As the direction of grain
boundaries in the channel region is set to the thickness direction
of the channel region, it is possible to increase the frequency
with which electrons pass through grain boundaries and reduce the
OFF current of the thin film transistor. This can be realized by
appropriately setting the laser light irradiation conditions (the
laser light irradiation energy density, the irradiation time and
the number of times of irradiation) for each of the openings a to
d. That is, the laser light irradiations conditions may vary
between the openings a to d.
[0073] FIG. 12 is a schematic view snowing a fourth example of the
openings 50 of the mask portion 40 of the present embodiment.
Opening regions 352a to 352d of the opening row B are similar to
the opening regions 152a to 152d of the second example shown in
FIG. 7. A difference from the second example is that opening
regions 351a to 351d of the opening row A have a rectangular shape
of the same size, and have generally the same vertical and lateral
dimensions as those of the region directly under the drain
electrode. Opening regions 353a to 353d of the opening row C have
an elongate shape of the same size, and have generally the same
vertical and lateral dimensions as those of the region directly
under the source electrode.
[0074] FIG. 13 is a schematic view showing an example of how grain
boundaries grow in regions that are annealed by the mask portion 40
shown in FIG. 12. As shown in FIG. 13, since the region directly
under the drain electrode and the region directly under the source
electrode are irradiated with laser light repeatedly (four times in
the example of FIG. 12 for the sake of illustration), the direction
of grain boundaries 14 is the thickness direction (the direction
from the near side toward the far side on the drawing sheet, i.e.,
the direction toward the gate electrode). In the region directly
under the drain electrode and the region directly under the source
electrode, the direction of grain boundaries is the direction
vertical to the drain electrode and the source electrode.
Therefore, the degree by which electrons are scattered by grain
boundaries is small, and it is possible to increase the ON current
of the thin film transistor.
[0075] Next, a laser annealing method using the laser annealing
apparatus 100 of the present embodiment will be described. FIG. 14
is a flow chart showing an example of a laser annealing method
using the laser annealing apparatus 100 of the present embodiment.
Hereinafter, the laser annealing apparatus 100 will be referred to
as the apparatus 100 for the sake of illustration. The apparatus
100 sets the mask 30 at a predetermined position (S11), and shoots
laser light (S12). The apparatus 100 moves the substrate 10 in the
scanning direction at a constant speed (S13). The laser light
source 70 shoots laser light at time intervals such that laser
light is shot each time an irradiation position of the substrate 10
arrives at a position corresponding to an opening 50 of the mask
30.
[0076] The apparatus 100 determines whether or not the substrate 10
has been moved to the final position in the scanning direction
(S14), and repeats the process of step 312 and subsequent steps if
the substrate 10 has not been moved to the final position (NO in
S14). If the substrate 10 has been moved to the final position in
the scanning direction (YES in S14), the apparatus 100 determines
whether or not a predetermined area of the substrate 10 has been
completely irradiated with laser light (3.1.5).
[0077] If a predetermined area of the substrate 10 has not been
completely irradiated with laser light (No in S15), the apparatus
100 moves the mask 30 by a predetermined distance (the dimension L
of the mask 30 in the lateral direction) in the direction
perpendicular to the scanning direction (516), and repeats the
process of step S12 and subsequent steps. If a predetermined area
of the substrate 10 has been completely irradiated with laser light
(YES in S15), the apparatus 100 ends the process. Note that the
substrate 10 is moved (transferred) in the scanning direction in
the example of FIG. 14, but the present invention is not limited
thereto. The substrate 10 may be fixed, and the mask 30 (optionally
including the optical system 60) may be moved in the scanning
direction.
[0078] Particularly, by performing partial laser annealing using
the mask 30 of the present embodiment, the crystal grain growth
direction (the direction of grain boundaries) by an SLS method can
be a plurality of directions on the substrate surface.
Microscopically, in the thin film transistor, the direction of
grain boundaries in the channel region may be varied from the
direction of grain boundaries in the regions directly under the
source electrode and the drain electrode. Thus, thin film
transistors for pixels and thin film transistors for driver circuit
area outside the display area, etc., can be freely arranged without
being restricted by the direction of grain boundaries, thus
increasing the degree of freedom in circuit design.
[0079] While the openings a, b, c and d are arranged in this order
in the scanning direction in the embodiment described above, the
present invention is not limited thereto, and the openings a, b, c
and d may be arranged in this order in the direction opposite to
the scanning direction.
[0080] While the shape of each of the opening regions of the
openings 50 is a rectangular shape in the embodiment described
above, the shape of an opening region is not limited to a
rectangular shape but may be an elliptical shape, for example. The
four corners of a rectangular opening region may be cut off in a
circular or rectangular shape. Then, it is possible to slightly
increase the amount of laser light irradiation in the vicinity of
the four corners of the opening region, and the region to be
irradiated with laser light can be shaped in a rectangular
shape.
[0081] The present embodiment can be applied not only to TFTs using
a silicon semiconductor but also to TFTs using an oxide
semiconductor, and it is possible to perform an annealing process
wherein the electron mobility is partially varied within one cycle
of scan.
[0082] A laser annealing apparatus according to the present
embodiment is a laser annealing apparatus including a mask having
an opening row, wherein the opening row includes openings each
including an opening region and arranged in a scanning direction,
for irradiating a substrate with laser light through the openings,
wherein a first opening including a first opening region and a
second opening including a second opening region are arranged next
to each other in a direction parallel to the scanning direction,
and the mask has a first opening row in which the second opening
region includes an opening region that is obtained by displacing a
region corresponding to the first opening region at the second
opening in a predetermined direction different from the scanning
direction.
[0083] A laser annealing method according to the present embodiment
includes: step A of providing a substrate having an amorphous
semiconductor film formed on a surface thereof; and step B of
selectively irradiating a portion of the amorphous semiconductor
film with laser light, wherein step B includes a step of
simultaneously forming, in said portion, a first melted region that
is elongated in a first direction and a second melted region that
is elongated in a second direction different from the first
direction.
[0084] A mask according to the present embodiment is a mask having
an opening row, wherein the opening row includes openings each
including an opening region and arranged in a scanning direction,
wherein a first opening including a first opening region and a
second opening including a second opening region are arranged next
to each other in a direction parallel to the scanning direction,
and the mask has an opening row in which the second opening region
includes an opening region that is obtained by displacing a region
corresponding to the first opening region at the second opening in
a predetermined direction different from the scanning
direction.
[0085] An opening includes one or more opening regions. An opening
row includes a plurality of openings arranged in a scanning
direction. Where N openings are arranged along one opening row, for
example, by shifting a substrate including a semiconductor film
formed thereon in the scanning direction, an intended region of the
semiconductor film is repeatedly irradiated with laser light N
times. The mask may include a plurality of opening rows.
[0086] A first opening including a first opening region and a
second opening including a second opening region are arranged next
to each other in a direction parallel to the scanning
direction.
[0087] That is, the first opening region a of the first opening and
the second opening region b of the second opening are arranged next
to each other in the direction parallel to the scanning direction.
Where the region corresponding to the first opening region a at the
second opening is denoted as the region a', the second opening
region b in the first opening row includes, at the second opening,
an opening region that is obtained by displacing the region a' in a
predetermined direction different from the scanning direction.
[0088] Assume that a semiconductor film is irradiated with laser
light through the first opening region a, and grain boundaries grow
in a predetermined direction in the region irradiated with laser
light. At the point in time for the next laser light irradiation,
laser light is shot through the second opening region b. In this
case, since the second opening region b includes an opening region
that is displaced from the region a' in a predetermined direction
different from the scanning direction, grain boundaries further
grow in the predetermined direction. Thus, grain boundaries can be
made to grow in intended directions, without being limited to the
substrate scanning direction.
[0089] In a laser annealing apparatus according to the present
embodiment, the mask has a second opening row in which the second
opening region includes an opening region that is obtained by
displacing a region corresponding to the first opening region at
the second opening in a direction parallel to the scanning
direction.
[0090] The opening region a of the first opening and the second
opening region b of the second opening are arranged next to each
other in a direction parallel to the scanning direction. Where the
region corresponding to the first opening region a at the second
opening is denoted as the region a', the second opening region b in
the second opening row includes, at the second opening, an opening
region that is obtained by displacing the region a' in a direction
parallel to the scanning direction.
[0091] Assume that a semiconductor film is irradiated with laser
light through the first opening region a, and grain boundaries grow
in the scanning direction in the region irradiated with laser
light. At the point in time for the next laser light irradiation,
laser light is shot through the second opening region b. In this
case, since the second opening region b includes an opening region
that is displaced from the region a' in a direction parallel to the
scanning direction, grain boundaries further grow in the scanning
direction. Thus, it is possible to produce a structure having
different grain boundaries on the same substrate. For example,
grain boundaries can be made to grow in different directions.
[0092] In a laser annealing apparatus according to the present
embodiment, the second opening region does not include a portion of
the region corresponding to the first opening region at the second
opening.
[0093] The second opening region b does not include a portion of
the region a' corresponding to the first opening region a at the
second opening. Thus, where laser light is snot through the second
opening, a crystalline semiconductor film corresponding to the
region a' can be prevented from being irradiated with laser light,
and it is possible to easily realize intended characteristics of
the crystalline semiconductor film.
[0094] In a laser annealing apparatus according to the present
embodiment, the second opening region includes a region
corresponding to the first opening region at the second
opening.
[0095] The second opening region b includes the region a'
corresponding to the first opening region a at the second opening.
Thus, where laser light is shot through the second opening, a
crystalline semiconductor film corresponding to the region a' can
also be irradiated with laser light, and it is possible to easily
realize intended characteristics of the crystalline semiconductor
film.
[0096] In a laser annealing apparatus according to the present
embodiment, the predetermined direction is a direction
perpendicular to the scanning direction.
[0097] The predetermined direction is a direction perpendicular to
the scanning direction. Then, it is possible to form, on the
substrate surface, grain boundaries extending in the vertical
direction and grain boundaries extending in the lateral
direction.
[0098] In a laser annealing apparatus according to the present
embodiment, the first opening region and the second opening region
each form a rectangular shape.
[0099] The first opening region a and the second opening region b
each form a rectangular shape. For example, in the first opening
row, the first opening region a and the second opening region b can
have a shape elongated in the scanning direction, and in the second
opening row, the first opening region a and the second opening
region b can have a shape elongated in a predetermined direction
different from the scanning direction. Thus, the direction of grain
boundaries can be an intended direction.
[0100] A display panel according to the present embodiment includes
a thin film transistor annealed by a laser annealing apparatus
according to the present embodiment.
[0101] It is possible to realize a display panel having thin film
transistors, wherein grain boundaries are made to grow in intended
directions, without being limited to the substrate scanning
direction.
[0102] In a display panel according to the present embodiment, the
thin film transistor includes: a gate electrode formed on a surface
of a substrate; a crystalline semiconductor film formed on an upper
side of the gate electrode; a source electrode formed on the
crystalline semiconductor film; and a drain electrode formed on the
crystalline semiconductor film, wherein a direction of grain
boundaries in the crystalline semiconductor film, which forms a
channel region between the source electrode and the drain
electrode, is parallel to a longitudinal direction of the channel
region, and a direction of grain boundaries in the crystalline
semiconductor film directly under the source electrode and the
drain electrode is different from the longitudinal direction.
[0103] The direction of grain boundaries of the crystalline
semiconductor film, which forms the channel region between the
source electrode and the drain electrode, may be parallel to the
longitudinal direction of the channel region, and the direction of
grain boundaries of the crystalline semiconductor film directly
under the source electrode and the drain electrode may be a
direction different from the longitudinal direction of the channel
region (e.g., the direction perpendicular to the longitudinal
direction).
[0104] In grain boundaries, electrons tend to be scattered,
resulting in a low electron mobility. In the channel region, since
the direction of grain boundaries is the longitudinal direction of
the channel region, the degree by which electrons are scattered by
grain boundaries is small, and it is possible to realize a large ON
current of the thin film transistor. The direction of grain
boundaries in the region directly under the source electrode and
the region directly under the drain electrode may be the direction
perpendicular to the longitudinal direction of the channel region,
for example, and it is then possible to increase the frequency with
which electrons pass through grain boundaries and reduce the OFF
current of the thin film transistor.
[0105] A display panel according to the present embodiment
includes: a first thin film transistor in which a direction of
grain boundaries in a crystalline semiconductor film, which forms a
channel region, is a predetermined direction; and a second thin
film transistor in which a direction of grain boundaries in the
crystalline semiconductor film, which forms the channel region, is
a direction different from the predetermined direction.
[0106] The display panel includes a first thin film transistor in
which the direction of grain boundaries in the crystalline
semiconductor film, which forms the channel region, is a
predetermined direction, and a second thin film transistor in which
the direction of grain boundaries in the crystalline semiconductor
film, which forms the channel region, is a direction different from
the predetermined direction (e.g., the direction perpendicular to
the predetermined direction). Then, thin film transistors of which
the longitudinal directions of the channel regions are
perpendicular to each other, for example, can be formed on the same
substrate. Therefore, the positions of the drain electrode and the
source electrode with respect to the channel region can be changed
freely in the vertical direction and in the lateral direction, and
it is possible to increase the degree of freedom in designing
circuits on the substrate.
[0107] The elements described in the examples above can be combined
with each other, and any such combination may bring forth a new
technical, feature.
[0108] The present application claims priority of Japanese Patent
Application No. 2018-143165, filed on Jul. 31, 2018, the entire
contents of which are hereby incorporated by reference.
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